1. Field of the Invention
The invention relates to a method for feeding call progress tones into conference connections in a pulse code modulation (PCM) time-division multiplex switching system, in the course of which overall sum code words are formed from PCM words supplied by the conference participants and intermediately stored in one-half of a conference memory and, if need be, converted into a linear code presentation, from which overall sum code words a plurality of differential partial sum code words are respectively formed by subtraction of one of the PCM words, the partial sum code words, after intermediate storage in the half of the conference memory, being respectively forwarded--if need be after re-conversion into non-linear code presentations--to that conference participant whose overall sum component they do not contain, whereas new PCM words arriving from the conference participants are intermediately stored in the other half of the conference memory, whereby the two halves of the conference memory alternately interchange their roles.
2. Description of the Prior Art
It is known for PCM time-division multiplex switching systems to generate the call progress tones upon employment of specific PCM words which are periodically emitted upon consideration of specific tone/pause programs and then respectively produce a specific call progress tone after digital/analog conversion on the receiving side (cf., for example, German OS No. 2,541,295).
In conference connections, the feeding-in of such digitally-generated call progress tones corresponds to the connection of a further conference participant. Accordingly, such call progress tones were heretofore simultaneously transmitted to all participants of the conference connection. For specific call progress tones, namely, for example, for the offering tone or the "knocking" tone, however, it is also of interest that the tone is only sent to specific participants of the respective conference participants.